We have not yet beat it, but we have gotten close. Here is the strategy we are working with, assuming we are reading the rules right.

I know it's been a couple of years since that post. I still wanted to say super thank you Lynx27! I couldn't have figured that one out myself, even when it seems pretty obvious after you realized it.

I played through all the scenarios of the GB boardgames when it came out. First I played them on my own, to be able to explain the rules to others later on. I played right until this very scenario. I tried it three times in a row with sort of improving strategies, and didn't even come close to stopping Vince and Zuul. (Not even the d8-instead-of-d6-as-Proton-dice house rule I made up and discussed on these forums helped any.) Then I quit, figuring I needed help by some of my tactically-inclined friends, with four brains being smarter than one and all that. Problem is, I couldn't get my gaming groups into the game so much that they made it to the fifth campaign. So I never encountered the "Who Brought the Dog" situation ever since the game came out.

Recently, I played through the whole game again with a friend. I didn't touch it in some time, and we liked it very much, we sorta breathed through one campaign after another, being very entertained. Then came the Spook Central campaign, ready to be tackled after all these years! We played the scenario two times and lost with no hope of snatching victory from the Terror Dog jaws at any time. Then we discovered Lynx27s post, followed it precisely, and, well ... we got farther to beating the game than ever before thanks to it.
We still lost in the third try, though ...!

I have some thoughts about this scenario: It seems correct that you have to blast Zuul into the gate when she's still adjacent to it, and hope, HOPE she will pop out inside the orange-lined squares. This is a chance roll. If you get the wrong number, you cannot win the scenario, because Zuul is going to move out of adjacency to the gate next ... and can just as well start all over! This pure chance roll, determining if you can win the scenario, is not even 50/50 – the chances are even slimmer than that!

And even if you do trap Zuul in the orange lined squares, it sure feels like if you do one false step, you still are going to lose. This mood could basically be very cool and dramatic, but in reality it's utterly frustrating, since the characters are not powered up yet, and it's the chance Proton rolls that lead to defeat, not bad tactics.